Drivers of Toyota Lexus 2004-10 RX 330/350 SUVs may come into your shop with a complaint of a rattling or buzzing sound that seems to be coming from the left portion of the instrument panel. Don’t be fooled, says Lexus, because there’s a good chance the noise is actually emanating from the other side of the firewall--at the brake booster check valve, to be exact. Replacing the check valve with an improved version should quiet things down.

To make a definitive diagnosis, go on the road and lightly accelerate the truck, then abruptly take your foot off the accelerator pedal. You can also duplicate the condition in the shop by depressing, then releasing the brake pedal with the transmission in Park. If you hear the rattle or buzz in either instance, that’s your cue that the original check valve is the source of the irritation and the new-design valve needs to be swapped in. Order Part No. 44730-20080 for valves with a straight nipple, 44730-14050 for valves designed with a 90º nipple.